The GPRS Network

Two new components have been added to the core network as the existing MSC’s are based upon the old circuit switched technology and cannot handle the new GPRS style data traffic. The two new components known as the GPRS support nodes are the serving GPRS support node known as the SGSN and the gateway GPRS support node known as the SGSN’s The SGSN itself can be viewed as a packet switched MSC as it delivers packets to mobile stations within its service area. SGSN send their queries the home location registers also known as HLR’s in order to obtain profile data of GPRS subscribers. The SGSN performs mobility management and is connected to the base station via a subsystem using a frame relay connection to the PCU in the BSC. The GGSN’s are used as actual interfaces to the external IP networks such as the public Internet along with other mobile service providers GPRS servers or even corporate Intranet’s. These systems maintain the routing information that is used to tunnel the protocol units to the SGSN’s. Other functions include the network and subscriber screening and address mapping. One of the GGSN’s may also be involved in providing support to several SGSN’s. The SGSN performs authentication and cipher setting procedures based on the same algorithms and encryption as the existing GSM. GPRS uses a ciphering algorithm which is optimised for handling packet data transmission.